The present invention relates to low viscosity polymer polyols that have a high hydroxyl number and a solids content of about 30 to about 65% by weight. This invention also relates to a process for the preparation of these novel polymer polyols. These polymer polyols have hydroxyl numbers of ≧20, solids contents of about 30 to about 65% by weight and a viscosity that is less than or equal to: be[2.7c]. These comprise the reaction product of a base polyol, a preformed stabilizer and at least one ethylenically unsaturated monomer, in the presence of a free-radical polymerization initiator and at least one polymer control agent.
Polymer polyol compositions are commercial products that have found use in a variety of applications primarily as constituents in the production of polyurethanes. Polyurethanes are suitable for the production of coatings, adhesives, sealants, elastomers, and flexible, semi-flexible and rigid foams. The primary function of polymer polyols is to enhance the hardness or stiffness of the polyurethane and, in particular, to enhance the load bearing or energy adsorbing capacity of polyurethane foams. End-use applications of polyurethane foams include, for example, mattresses, furniture, carpet pad; packaging and energy management, thermal insulation, and automotive seating, trim, headliners, sound insulation, crash pads, etc.
The basic patents relating to such polymer polyol compositions are Stamberger, U.S. Pat. Re. 28,715 (reissue of U.S. Pat. No. 3,383,351) and U.S. Pat. Re. 29,118 (reissue of U.S. Pat. No. 3,304,273). As described therein, a stable dispersion of polymer particles in a polyol can be produced by polymerizing one or more ethylenically unsaturated monomer dissolved or dispersed in a polyol in the presence of a free radical catalyst.
Initially, the primary polymer polyol compositions accepted commercially used acrylonitrile in its manufacture. Many of these compositions possessed undesirably high viscosities for certain applications. More recently, acrylonitrile-styrene monomer mixtures have been used commercially to make the polymer component of polymer polyols. The expanding demand for polymer polyols has highlighted several product needs and this has spawned additional advances in technology.
Polymer polyols derived from such high styrene monomer mixtures appear incapable of satisfying ever-increasing market needs, which include rigorous stability, filterability and low-viscosity requirements, and increased load-bearing characteristics in polyurethane foams. It is known that polyurethane foams with increased load-bearing characteristics can be obtained by increasing the polymer or solid contents and/or by increasing the functionality and hydroxyl number of the polyol. Thus, polymer polyols having high solids contents, i.e. 30 to 60 weight percent or higher, are desirable. However, an increase in the solids contents of polymer polyols is, generally, at the expense of the other properties (i.e. filterability, stability and viscosity) of the polymer polyol. It is desirable that polymer polyols have high solids contents, with relatively low viscosities, and good filterability.
Employment of high styrene monomer mixtures and high solid content polymer polyols, by prior practices, generally resulted in undesirably high viscosity polymer polyols. The viscosity of a polymer polyol should be sufficiently low for ease of handling during its manufacture. In addition, the viscosity should facilitate transport, handling and, ultimately, adequate processability, in the employed foam processing equipment. Because of increased use of sophisticated mixing systems, such as impingement systems, excessive viscosity of the polymer polyol is becoming a significant problem. The need for lower viscosity polymer polyols is apparent to satisfy these increased demands in the art.
As indicated, polymer polyol stability is a concern to makers of polyurethanes. At one time, seediness or filterability, a measure of stability of polymer polyols, was not a major issue in commercial practices. However, advances in the state of the art of polyurethane production such as high pressure carbon dioxide injection have resulted in revisions in polymer polyol stability and filterability criteria.
With commercial developments in sophisticated, high-speed and large-volume equipment and systems for handling, mixing and reacting polyurethane-forming ingredients have evolved the need for highly stable and low viscosity polymer polyols. Polymer polyols have certain minimum requirements for satisfactory processing in such sophisticated foam equipment. Typically, the prime requirement is that the polymer polyols possess sufficiently small particles so that filters, pumps and the like do not become plugged or fouled in relatively short periods of time.
Though there have been advances in reduction in viscosity and increase in solids of polymer polyols, there remains a need for improvement in viscosity reduction and increase in solids content. Greater reductions in viscosity are needed to meet market demands and greater effective increases in solids content are also needed by the market. More importantly, there is a need for technology in polymer polyols that maximizes viscosity reduction while also providing a viable mechanism to higher solids content.
U.S. Pat. No. 4,522,976 discloses polymer polyol dispersions in a mixture of low molecular weight polyols and polyether polyols, and the suitability of these dispersions for preparing foams. These polymer polyols are prepared by polymerizing 25 to 70% by weight of one or more ethylenically unsaturated monomers in a polyol mixture comprising (1) 25 to 99% by wt. of a polyol containing from 2 to 8 hydroxyl groups and having an equivalent weight of 30 to 200, and (2) from 1 to 75% by wt. of a macromer containing induced unsaturation.
Polymer polyols dispersions and a process for their production are also disclosed in U.S. Pat. No. 4,690,956. These polymer polyol dispersions are prepared by free-radical polymerization of an ethylenically unsaturated monomer or monomers in the presence of a reaction moderator in a polyol mixture of polyether polyol and a macromer which contains induced unsaturation. The reaction moderator has a fumarate containing polyetherester polyol as the unsaturation moiety, and at least 50% of the ethylenically unsaturated monomer is acrylonitrile.
Surprisingly, it has now been found that the good stability and filterability of a polymer polyol can be achieved at a very high solids level in a base polyol having a high hydroxyl number. In accordance with the present invention, the combination of high hydroxyl number/low molecular weight base polyols with a preformed stabilizer in a polymer polyol result in the final product having a significantly lower viscosity.